If you don't have anything important on the computer , i would suggest you just reinstall it,
But if you need to save stuff you'll need to do some work on it , and it will wreck your Brain as fixing software is a nightmare even for those in the know
If you what to try to fix it , you need to boot into safe mode By Hitting F8 then selecting safe mode,
and Run Some computer doctoring programs.
like
AVG Free
Ewidow
Ad-aware
Spy-bot